"Soldering" copper pipe to aluminium plate (2mm thick)

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Peter

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Anyone done this. If yes how.
Have tried using ordinary plumbing solder and flux. Solder stuck to pipe but run off aluminium.
 
The obvious question is why do it? It is a near impossible joint to make. There are special aluminium solders that will join aluminium to aluminium, but they really work by melting the surface of the parts being joined and forming a weld using the filler rod which has a lower melting point and alloys with the parts being joined. If you really need to fix the copper pipe to an aluminium plate then solder (or silver solder) a disc of copper to the pipe and bolt it to the plate.
 
JumbleDuck said:
"Durafix" welding rods are advertised as suitable for copper to aluminium:

http://www.oxfordweldingsuppliesltd...-rods/durafix-easyweld-aluminium-welding-rods
Click to expand...

I had not come across those Durafix rods before. I have used Lumiweld rods but don't think they work with copper and need a higher temperature. I notice that they come with a "micro stainless steel brush" which indicates that they probably work the same way as Lumiweld. To "solder" aluminium alloys you need to break down the oxide layer that forms on the alloy as soon as you cut it. To do so you need to heat it to above the melting point of the solder rod, then remove the heat souse, apply the rod so that it melts and quickly scratch though it to abrade the oxide layer so that the filler rod can alloy with the aluminium alloy. Lumiweld supplied a stainless steel rod with a sharp end to do the scratching and a stainless brush to clean the aluminuim beforehand. You need the parts firmly held to enable you to wield the blowlamp, apply the filler and scratch through it to make the weld. If you do try it let us know how it went.
 
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I've seen a lot of tin and silver plated aluminium, you could solder to that.
But I think I'd get an ali tube tig welded to the plate instead?

I have personally welded copper to aluminium, but this wasn't seen as a good thing at the time!

I think brazing and silver soldering are possible, but to get this kind of thing right you need lots of practice with 'ordinary' work in these processes IMHO. So maybe not a good DIY route if it's something that matters.
 
JumbleDuck said:
"Durafix" welding rods are advertised as suitable for copper to aluminium:

http://www.oxfordweldingsuppliesltd...-rods/durafix-easyweld-aluminium-welding-rods
Click to expand...

There was an article in PBO a few years back about soldering aluminium. The biggest prob is the instant oxidation after cleaning. They used a zinc filler. They then tested with salt water and it reacted with the zinc and basically dissolved it!
So, it can be done but salt water melts it and as for copper, zinc and aluminium as a producer of electric!
 
Peter said:
Anyone done this. If yes how.
Have tried using ordinary plumbing solder and flux. Solder stuck to pipe but run off aluminium.
Click to expand...

Copper and aluminium will react very strongly if you add a bit of humidity however minimum it will work as the electrolyte. Aluminium is very susceptible to galvanic corrosion if in contact with copper.

You can get tined Copper when that needs to happen and it can help prevent galvanic corrosion but not stop it completely. I believe there is also Silver Flashed copper for the same purpose.
You can remove the Aluminium oxide in the area you wish to weld by simply sanding it and giving you about 8m until a new layer has been formed on the surface. But by doing that you’re also removing the oxide and exposing the aluminium to the copper, with the galvanic reaction starting at that point. The Oxide serves as a barrier that you will be removing.
As to welding it. Tig, brazen, mig, torch, E. You can use a filler of the same material (copper) or use aluminium/bronze filler with pure Helium for best results on AC. I would pulse it at 36 Pps. But it’s a bit more demanding. DC negative 80/20 Ar/He safest bet.

The Oxide has a melting point of 2,072 Celsius and the Aluminium 660 Celsius. Copper melting point is around 1000 Celsius top of my head, makes for an interesting combination to weld.
If you care to try it, warm every part to about 300/400 Celsius with a torch before you weld. IF, however you are thinking of a pipe to carry water or gas. THAT is NOT something you should do. But hey.

Deoxidized Copper rod is recommended for welding copper. Different materials, Silfabronze, BOC Silicon Bronze CZ6 Rod.

As I don't really know what part you are trying to weld, dimensions and diameters, these are some of the basics.
 
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